Transcript Signal Types and Transmission Media

G055 - Lecture 07
Signal Types and Transmission Media
Mr C Johnston
ICT Teacher
www.computechedu.co.uk
Session Objectives
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Be able to describe different types of signal used to transmit
data on a network
Know types of cable used to transmit data and the correct
connector type for each,
Understand how fibre optical and wireless transmission
methods work.
Types of Signal
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Digital Signals are a series of pulses – either 1 or 0,
Figure 1: A Digital Signal
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Computers operate using digital – therefore the signals
generated are also digital,
To transmit them an interface card is needed to change the
signals into a frequency which represents the 1s and 0s on
the communication medium - this is known as modulation,
When a computer receives a signal it needs to be translated
from the frequency into 1s and 0s which the computer can
understand – this is known as demodulation.
Analogue Signals
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Analogue signals are a continuous wave pattern,
Figure 2: An Analogue Signal
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Some transmission medium can only carry analogue
frequencies rather than digital,
If digital data is going to be transmitted on a medium that
can only carry analogue signals, then it has to be converted
into a set of analogue signals,
The signals are modulated from digital to analogue and
demodulated at the other end,
A device called a modem is responsible for this.
Diagram Showing Modem Use
Computer In Coventry
Email
Composed
And Sent
Modem
Digital Signal
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Public
Computer In London
Telephone
Email
System
Received
Modem
And Read
Analogue Signal
Digital Signal
Newer digital phone lines don’t need a modem as they are
able to accept digital frequencies
Common Cables
1
Cable Type
Connector Overview
Unshielded Twisted Pair (UTP)
RJ-45
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Shielded Twisted Pair (STP)
RJ-45
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4 sets of twisted pairs with an outer case,
Twisted pairs reduce electrical interference,
Cheap, easy to work with as its flexible fast with data
speeds up to 1000mb/s
Still prone to electrical interference which causes data
to do missing.
4 sets of twisted pairs, covered with a layer of metal
foil and an outer case,
Twisted pairs reduce electrical interference,
Foil layer further reduces electrical interference making
it more reliable than UTP,
Slightly nearer and less popular as UTP
Cheap, easy to work with as its flexible fast with data
speeds up to 1000mb/s
Still prone to electrical interference which causes data
to do missing.
Common Cables
2
Cable Type
Connector Overview
Coaxial cable
BNC (Bayonet
NeillConcelman)
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Solid copper cable covered in an insulating plastic case.
The case is then covered with a copper mesh which is
all encased with another plastic sleeve,
Very little interference,
Less flexible then UTP as thicker,
Frequently used from road to box for cable broadband,
Available in different thicknesses but thinner cables
have shorter cable runs.
Telephone cables also use twisted pairs with a smaller RJ11 connector on – typically there are only 2 sets of pairs.
Fibre Optics
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Uses pulses of light rather than electrical signals to transmit
the data – therefore is immune to electrical interference,
The light is pulsed down hollow glass or plastic tubes – main
advantage is distance and speed - 14 Tera bits per second
over a single 160 km long optical fiber is the current record.
(http://www.ntt.co.jp/news/news06e/0609/060929a.html)
Cable Type
Connector
Overview
Fibre Optic Cable
SC (subscriber connector)
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or
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ST (straight tip)
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Hollow glass or plastic tube which light is pulsed down,
Has a protective cover to protect the light from
interference and is immune to electrical interference,
Glass can carry longer than plastic,
Can travel long distances and is fast
Expensive over short distances but very economical
over long
Wireless Transmission
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Wireless networks uses radio signals to transmit data, so no
wiring is required,
Wireless Access Points are cabled to the main network and
broadcast / receive data via radio waves at a particular
frequency,
A wireless network card required in each client to receive /
send the radio signal
Radio waves are subject to interference from signals that just
hang around in the air, and it can be slow and unreliable.
It is possible that signals can be received outside the area they
are intended for, causing some problems with security,
Typical speeds 11 Mb/s to 54 Mb/s - 802.11n up to 600Mb/s,
RJ-45 Wiring Diagram
Topic Exercise
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Complete the following reading:
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A2 Text Book Pages pg21-23 (start @ connections in a network
heading)
AVCE Unit 08 Book pg44-46
Have a go at creating your own STP / UTP cable use the
wiring diagram to help and test with the cable tester,
Have a go at creating your own coax cable – we don’t have
any BNC connectors but the TV ones are similar,
Download and complete this topics past exam paper
questions – complete for next lesson.